1. Field of the Invention
The present invention generally relates to a protection providing method for setting a primary provider edge apparatus and a secondary provider edge apparatus with a customer edge apparatus in a network configuration where the customer edge apparatus is redundantly connected to a first provider edge apparatus and a second provider edge apparatus, and a customer edge apparatus thereof.
2. Description of the Related Art
A technology referred to as MPLS (Multi-Protocol Label Switching) is drawing attention as a recent packet transmission technology. MPLS is a technology that realizes high speed transmission by applying a label to a packet. In the IETF (Internet Engineering Task Force), studies are being conducted on PWE3 (Pseudo Wire Emulation Edge-to-Edge) which uses MPLS as a pseudowire (PW: Pseudowire) and provides existing services (e.g., FR (Frame Relay), ATM (Asynchronous Transfer Mode), TDM (Time-Division Multiplexing), Ethernet (Registered Trademark) from end-to-end (point-to-point). Since MPLS can be used as a pseudowire for merging various services, MPLS is anticipated to be utilized for carrier networks.
FIG. 1 shows a reference model of PWE3 model described in RFC (Request For Comment) 3916 and RFC 3985. The reference model PWE3 includes a customer edge apparatus used by a user for accessing a provider (referred to as CE (Customer Edge) apparatus) CE1, CE2 and a provider edge apparatus (referred to as PE (Provider Edge) apparatus) PE 1, PE2. The PE apparatus is connected to the CE apparatus via an attachment circuit and also to a P (Provider) apparatus serving as the backbone of the provider.
In order to provide the End-to-End service via a PSN (Packet Switched Network), a virtual tunnel referred to as a PSN (Packet Switched Network) tunnel is established between the PE apparatus PE1 and the PE apparatus PE2. In order to create this tunnel, MPLS or a technology referred to as L2TP (Layer 2 Tunneling Protocol) can be used. Then, by establishing the pseudowires PW1, PW2 inside the tunnel, End-to-End services can be provided between the CE apparatus CE1 and the CE apparatus CE2.
As described above, since the MPLS provides End-to-End services and is anticipated to be utilized for carrier networks, high reliability is desired. In order to achieve high reliability, there is a need for a technology, so called protection technology, that provides a line to be used as a secondary line in a case where failure occurs in a transmission path or a communication apparatus.
As for existing protection technology, there is protecting of a path between PE apparatuses (i.e. LSP (Label Switched Path). One example of the technology is a Fast Reroute (RFC 4090) in which data are routed around a primary LSP to access a secondary LSP when a failure occurs in the primary LSP. As an exemplary technology for switching from a primary LSP to a secondary LSP, a secondary LSP is set beforehand so that a path can be searched and a LSP can be switched to a secondary LSP when a failure occurs, as described in Japanese Laid-Open Patent Application No. 2002-374288.
However, this protection technology is to be applied to a redundant configuration of a path between PE apparatuses as shown in FIG. 2(a) but not a redundant configuration of a path between PE apparatuses as shown in FIG. 2(b). In other words, this protection technology is not configured to allow CE apparatuses CE1, CE2 to switch from main use PE apparatuses PE1a, PE2a to auxiliary PE apparatuses PE 1b, PE 2b. 
In order to provide the redundant configuration of the PE apparatuses shown in FIG. 2(b) by using a related art example, the CE apparatuses CE1, CE2 require a technology that selects a primary PE apparatus and a secondary PE apparatus (or a primary pseudowire or a secondary pseudowire) and a technology that provides protection in view of the End-to-End service between the CE apparatus CE1 and the CE apparatus CE2.
In a case where Ethernet (Registered Trademark) is used as the End-to-End service, a spanning tree protocol may be applied to the loop path having a redundant configuration of PE apparatuses as shown in FIG. 2(b). Although protection can be provided by using this spanning tree protocol, the time required for switching is performed in units of a few seconds. Therefore, it is difficult to perform high speed switching from a primary PE apparatus to a secondary PE apparatus.
In a case where TDM is used as the End-to-End service, there is no protection technology as APS (Automatic Protection Switching) defined in SDH (Synchronous Digital Hierarchy). Therefore, it is necessary to perform switching from a primary PE apparatus to a secondary PE apparatus manually. Thus, it is difficult to perform high speed switching from a primary PE apparatus to a secondary PE apparatus.
In a case where ATM is used as the End-to-End service, switching can be performed by using a protection technology referred to as linear protection according to ITU (International Telecommunication Union). However, in a case of providing protection referred to as 1:1 Bidirectional, a primary PE apparatus and a secondary PE apparatus may not match. Furthermore, in a case where the mismatch occurs, it becomes necessary to manually perform recovery. Therefore, it is difficult to reliably perform high speed switching from a primary PE apparatus to a secondary PE apparatus.
Furthermore, in a case of providing protection to a redundant configuration of PE apparatuses, operations by a CE apparatus differ depending on the End-to-End service. Therefore, in a case where plural services are installed in a pseudowire, operations by the CE apparatus become complicated.
Therefore, it is difficult to provide reliable high speed protection to a redundant configuration of PE apparatuses.